Dispensing device

ABSTRACT

An inhaler, comprising an electrohydrodynamic comminution means, a means for partially or fully discharging the liquid comminution and a conduit through which the liquid comminution is administered, wherein the discharging means is arranged to be activated by inhalation of the user.

This is a Continuation of U.S. Ser. No. 08/492,204 filed Jun. 2, 1995,now Pat. No. 6,105,571 which is in turn a continuation of Ser. No.PCT/GB93/02634 filed Dec. 22, 1993.

The invention relates to a dispensing device for comminuting a liquidand the uses of such a device, especially in medicine.

Dispensing devices are known which produce a finely divided spray ofliquid droplets by electrostatic (more properly referred to as‘eletrohydrodynamic’) means. The droplet spray in such devices isgenerated by the application of an electric field to a liquid at a sprayhead or spray edge. The potential of the applied electric field issufficiently high to provide comminution of the liquid from the sprayhead. The droplets produced are electrically charged and thus areprevented from coagulating by mutual repulsion.

Electrohydrodynamic sprayers have potential uses in many areas,including agriculture and the automotive industry and also fordispensing cosmetics and medicines.

United Kingdom patent number 1569707 describes such anelectrohydrodynamic spray device principally for use in crop spraying.

United Kingdom patent number 2018627B discloses an electrohydrodynamicspray device wherein the charged droplet spray is fully or partiallyelectrically discharged by means of an earthed electrode having a sharpor pointed edge and located downstream of the spray head. EuropeanPatent number 0234842 also uses this technology and relates to aninhaler in which charged droplet spray is discharged prior to inhalationby means of a sharp or pointed discharge electrode carrying an oppositecharge to the droplet spray and located downstream of the spray head.The droplets are discharged to facilitate droplet deposition into therespiratory tract by preventing deposition of charged droplets onto themouth and throat of the user.

A common feature of all known electrohydrodynamic spray devices is thatthe electric charge used to generate the spray is applied directly tothe spray head. It has now surprisingly been found that the directapplication of the field is not essential and that theelectrohydrodynamic comminution of a liquid may be accomplished byinducing the required electric charge at the spray head. In addition andadvantageously, it has been found that the comminutions produced can bepartially or fully discharged prior to use.

This method of induced charging has been found to provide bettercomminution of liquids having lower electrical resistivity.

Accordingly, it is one aspect of the invention that there is provided anelectrohydrodynamic dispensing device for comminuting a liquid, whereinthe liquid is comminuted by an induced electrical charge.

The dispensing device normally comprises a comminution site, a means forsupplying liquid to the comminution site and a means for inducing anelectrical charge at the comminution size sufficient to comminute theliquid.

The comminution site may be any conventional electrohydrodynamiccomminution site such as a surface or edge generally provided by a thincapillary tube, a nozzle or a slot defined by two parallel plates.

Appropriate means for supplying liquid to the comminution site includemechanical or electrically powered pumps which are capable of providingthe required flow rate of liquid to the comminution site such as asyringe pump or the electrically powered pump described in EP 0029301.

The comminution means of the invention can be used with a large range offlow rates, but generally operates with flow rates in the range ofbetween 0.1 to 500 μl L per second, such as 0.5 to 5 μL per second,especially for inhaled administration, or 10 to 200 μL per second,especially for agricultural use.

The means for inducing the electrical charge at the comminution site maybe any conventional source of electrical charge which in use is capableof inducing a charge sufficient to comminute the liquid from thecomminution means including a high voltage generator or a piezo-electricgenerator. The charge required is usually of the order of 1-20 kilovoltsfor example 10 kilovolts.

After formation of the liquid comminution, the electrically chargedliquid droplets are attracted towards and will impact the means forinducing the electrical charge at the comminution site. In a preferredaspect of the present device, there is therefore provided a means forpartially or fully electrically neutralising the liquid comminutionbefore it impacts the induced charging means. One suitable means forpartially or fully electrically discharging the liquid comminution is asharp or pointed discharge electrode located downstream of thecomminuted liquid.

The sharp or pointed discharge electrode may be earthed or it may bemaintained at a polarity opposite to that of the induced charging meansby connection to a suitable charging means. In either case thecomminuted liquid is partially or fully discharged by a cloud of chargedions produced from the surrounding air having an opposite electricalcharge to that on the comminuted liquid spray. The ion cloud isattracted towards, collides with and thereby partially or fullydischarges the liquid spray.

In one particularly advantageous form of the device, the means for fullyor partially discharging the liquid comminution is provided by acombination of the sharp or pointed discharge electrode and at least onecapacitor, the capacitor acting to absorb the charge from the gaseousions from the sharp or pointed discharge electrode until the inducedcomminution of the liquid is established, the capacitor is arranged toabsorb the ions until it reaches a predetermined potential at whichpotential it ceases to absorb the ions thereby allowing them topartially or fully discharge the liquid comminution.

Generally, the capacitor is chosen to have a time constant having thesame order as the time required to establish the liquid comminutionspray cloud. Thus the time constant will have a value, in seconds, whichis the product of the capacitance, C and the resistance, R, of thecapacitor.

The value of CxR for the capacitor is chosen so that the capacitor willcharge until it reaches a prearranged potential sufficient to modify theelectric field, the capacitor then discharges towards the establishedspray cloud. Generally, the time-constant required will be of the orderof seconds or a number of milliseconds. For example, a capacitor of 0.1microfarad with a resistance of 10 megohms will produce a time constantof one second.

In yet a further aspect, the means for fully or partially dischargingthe liquid comminution is provided by an electrode arranged to have afirst surface capable of producing an electric field sufficient toinduce the required charge for liquid comminution in the comminutionmeans and also to impart sufficient inertia to the liquid comminution sothat it substantially bypasses the first surface, the electrode alsohaving a second surface capable of producing an ionic discharge to fullyor partially discharge the liquid comminution.

Generally, the second surface is shaped to have a sharp edge or a pointwhich in use produces the ionic discharge.

Suitably, the electrode is an annular electrode coaxially located withrespect to the intended flight path of the liquid comminution, in use,the upper surface of the annular electrode induces the required chargein the comminution means, the lower surface being shaped so as toproduce the ionic discharge.

In operation the field pattern of the upper surface of the annularelectrode is such that the comminution is directed onto an axial flightpath with respect to the annular electrode and is provided withsufficient inertial force to substantially bypass the first surface, thecomminution is then fully or partially discharged by the gaseous ionsproduced by the second surface.

The device of the invention may be used to dispense liquids comprisingcomponents useful for human or animal health care, such as medicamentsfor pharmaceutical or public health care use or medically usefulcompounds such as anesthetics.

Suitable liquids include liquids comprising components for agriculturaluse such as pesticides or biocides.

Suitable liquids include liquid cosmetic formulations.

Other suitable liquids include paints and inks. Also included areliquids for providing aromas.

Preferred liquids are pharmaceutically active liquids.

The communition means of the dispenser provides liquid droplets withinthe range of from about 0.1 to about 500 microns in diameter. Moreusually from 0.1 to 200 microns, such as 1.0 to 200 microns: Examplesinclude droplets within the range of 5.0 to 100, 0.1 to 25, 0.5 to 10 or10 to 20 microns. A favoured range for inhaled administration is 0.1 to25 or 0.5 to 10 microns, especially for administration to the lowerrespiratory tract, and 10 to 25 microns, especially for administrationto the upper respiratory tract.

For a given liquid the diameter of the droplets can be controlled byvarying the applied voltage and liquid flow rate using routineexperimental procedures.

Liquids having viscosities within the range of from 1 to 500 centipoiseand resistivities in the range of from 10²-10⁸ ohm m can be comminutedby the present device.

As stated this method of induced charging has been found to providebetter comminution of liquid having a lower electrical resistivity, suchas is the case of aqueous solvents, including solvent mixtures, andsolutions thereof and low resistivity organic solvents such as alcohols.

One favoured use of the device of the invention is for the dispensationof a comminuted liquid for inhalation.

Accordingly, in one preferred aspect of the invention there is provideda device for comminuting a liquid for inhalation, wherein the liquid iscomminuted by an induced electrical charge.

The device of the invention may be adapted into any embodiment formwhich dispenses comminuted liquid for inhalation, for both medicinal andnon-medicinal use.

Non-medicinal inhalation uses includes dispensing perfumes and aromas.

Preferably, the device is in the form of an inhaler, for the inhaleddelivery of a medicament.

A preferred liquid is therefore a liquid medicament formulation adaptedfor inhaled administration.

Medicaments suitable for adaption for inhaled administration includethose used for the treatment of disorders of the respiratory tract, suchas reversible airways obstruction and asthma and those used in thetreatment and/or prophylaxis of disorders associated with pulmonaryhypertension and of disorders associated with right heart failure byinhaled delivery.

One problem associated with inhalers is coordinating the release of theliquid spray with inhalation by the user. It is a further aspect of thepresent invention that there is provided a means which facilitates thisproblem.

Accordingly, there is also provided an inhaler, comprising anelectrohydrodynamic comminution means, a means for partially or fullydischarging the liquid comminution and a conduit through which theliquid comminution is administered, wherein the discharging means isarranged to be activated by inhalation of the user.

Suitably, the electrohydrodynamic comminution means comprises acommunition site and a charging means, the charging means actingdirectly or by induction to produce the required charge on thecommunition means, favourably acting by induction.

Suitably, the electrohydrodynamic communition means comprises a meansfor supplying liquid to the communition means.

One favoured arrangement wherein the discharging means is activated byinhalation of the user comprises a valve means located so as to open andclose the conduit, suitably within the conduit, the valve means beingopened by inhalation of the user which then activates the dischargingmeans.

A suitable discharging means is provided by one or more capacitors or bya sharp edged or pointed electrode.

When the discharging means is a sharp edged or pointed electrode, thedischarging means is preferably operationally attached to the valvemeans such that when the valve means opens the sharp edged or pointedelectrode is thereby exposed to the communited liquid.

A suitable valve means is a flap valve.

In a particular instance the sharp edged or pointed electrode is fixedso as to extend upwards from the plane of the flap valve, the flap valvebeing pivotally fixed so as to open and close the conduit, such thatwhen the flap valve pivots open the sharp edged or pointed electrodepivots into the flight path of the comminuted liquid.

Thus in a most particular instance the invention provides an inhaler,the inhaler comprising an electrohydrodynamic comminution site, a meansfor supplying liquid to the comminution site, a means for charging thecomminution site, a sharp edged or pointed electrode for partially orfully discharging the liquid comminution and a conduit through which theliquid comminution is administered, the conduit having a valve meansactivated by inhalation of the user, wherein the valve means comprises aflap shaped to seal the conduit, the flap being pivotally fixed so as toopen and close the conduit, the sharp edged or pointed electrode extendsupwards from the plane of the flap valve, such that in use the flapvalve pivots open and the discharging means pivots into the flight pathof the comminuted liquid.

When the devices comprise a sharp edged or pointed electrode, thearrangement suitably provides that the sharp edged or pointed electrodeis electrically shielded from the liquid comminution when the valvemeans is closed. One particular method of achieving this is that thesharp edged or pointed electrode pivots into a recess formed in thecharging means when the valve means closes.

When used herein ‘a comminution’ includes a liquid droplet spray.

When used herein ‘medicament’ includes proprietary medicines,pharmaceutical medicines and veterinary medicines.

When used herein, unless more specifically defined herein, ‘inhaledadministration’ includes administration to and via the upper respiratorytract, including the nasal mucosa, and the lower respiratory tract.

The description ‘sharp edged or pointed’ when used herein in relation tooperational parts of the device, such as the electrode, also includeselectrical equivalents thereof and hence includes shapes such as ridgesand the like. The essential requirement is that the operational part ofthe device has, or a component or feature of the device has, dimensionswhich will give rise to a sufficiently high electrical field strength soas to exceed the breakdown strength of the air. This tropic istheoretically described in “Depositional Control of MacroscopicParticles by High Strength Electric Field Propulsion” by R A Coffee, in“Transactions of the Institution of Electrical and Electronic Engineers,Industry Applications, USA”, Vo. IA-10 pp 511 to 519, July/August 1974.An example is an electrical field strength of approximately 3 millionvolts per meter.

The liquid medicinal formulations for use in the device of the inventionmay be formulated according to conventional procedures, such as thosedisclosed in the U.S. Pharmacopeia, the European Pharamcopoeia, 2ndEdition, Martindale The Extra Pharmacopoeia, 29th Edition,Pharmaceutical Press and the Veterinary Pharmacopoeia.

The liquid cosmetic formulations for use in the device of the inventionmay be formulated according to conventional procedures, such as thosedisclosed in Harry's Cosmeticology, 9th Edition, 1982, George Goodwin,London.

BRIEF DESCRIPTION OF DRAWINGS

FIGS. 1 and 2 illustrate a device with a hinged flap which effectsdroplets ionization;

FIG. 3 shows a side view of a device which uses electrically floatingconducting surfaces to effect droplet charge;

FIG. 4 shows a side view of a device with an induction ring;

FIGS. 4 a and 4 b show modifications of the device shown in FIG. 4; and

FIG. 5 illustrates a device which uses a controlled field modificationtechnique to both discharge and recharge droplets to an optimal value.

The invention may now be described, by way of illustration, withreference to the accompanying FIGS. 1 to 5.

In FIGS. 1 and 2, a device of the invention is illustrated in which apressure reduction created by the action of breathing through a suitableducting (1) causes a lightweight flap (2), balanced by a second member(3) pivoted at a hinge (4) and connected to a dc high voltage supply ofeither polarity (5) to revolve through a sufficient degree of arc toallow the second member of the flap to become exposed to the electricfield and then create gaseous ions.

The flap value thus has two actions: (a) it opens an air passage (1) tofacilitate a flow of droplets; and (b) it simultaneously rotates abalancing member (3) attached to the flap (2) through a sufficientdegree of arc to expose a ridge, or nipple (6) having one dimension ofless than about 1.0 mm radius of curvature.

The ridge, or nipple (6) may be made of any conducting, orsemi-conducting material such as metal, or carbon-loaded plastic, and isconnected to a source of high voltage (5). When not actuated bybreathing, the ridge will be electrically screened by the surface of aflat electrode (7), also connected to the high voltage source (5). Inthis position the electrode (7) may be switched on, or off by a simpleswitch (8).

When switched on, the electrode induces a potential of opposing polarityat the tip of a nearby nozzle (9). This induced potential causes liquidat the tip of the nozzle to emerge as a fast jet which breaks up intocharged droplets. The nozzle (9) is connected to earth.

The invention therefor performs more than one function: (a) the flapvalve (2) allows droplets to be inhaled only when the valve is actuatedby the act of breathing; (b) the principle of induction, rather thandirect nozzle charging improves the control of droplet size and maximumflow rate, for those liquids which are difficult to atomize by theelectrohydrodynamic process; (c) it overcomes the inevitableconsequences of induction charging, which is that the opposite polaritydroplets would otherwise be so strongly attracted to the source of theinduced voltage (7) that the droplets would not be available fordelivery by inhalation, or other forms of deposition onto targetsurfaces.

In FIG. 3, one or more electrically floating conducting orsemi-conducting surfaces (10), attached to one or more capacitors (11)are used to attract and capture the gaseous ions so that the electricfield created by the electrode (6) acts directly upon the nozzle (8)without impingement of gas ions. Such gas ions, if allowed to reach thenozzle unimpeded would be expected to modify the electric fieldsurrounding the nozzle so as to prevent the emerging liquid from formingthe necessary jet of liquid for atomization by the electrohydrodynamicmethod. The capacitor(s) is chosen to have a time constant of the sameorder as the time required to established a spray cloud. This timeconstant will have a value, in seconds, which is the product of thecapacitance, C and the resistance, R, of the capacitor. The value of CxRis thus chosen so that the capacitor will charge by bombardment ofgaseous ions, until it reaches a sufficient potential to modify theelectric field and to re-direct the ions toward the established spraycloud. Generally, the time-constant required will be of the order ofseconds or a number of milliseconds. For example, a capacitor of 0.1microfarad with a resistance of 10 megohms will produce a time constantof one second. FIG. 3 shows one configuration that will create therequired induction potential at the nozzle when the electrode (7) isenergized and, after a suitable period, dependent upon the position andtime constant of the capacitor(s) will then re-arrange the field toallow gaseous ions to migrate into the spray cloud so as to modify thecharges on all droplets to a lower (optimal) or approximately zerovalue. Such droplets may then be readily inhaled.

The charged droplets are prevented from impinging upon the high voltageelectrode (7) by the action of fast moving gaseous ions. These ions arecreated by the combination of electrode voltage, say one to tenkilovolts dc, and the radius of curvature of the small dimension of theridge or nipple (6) on the balancing member (3) and by juxtaposition ofthe nozzle (9), the electrode (7) and the capacitor(s) (11). Thecapacitor(s) (11) may be used to increase the degree of control of theshape of the field and the timing of the essential reshaping process.

Liquid is supplied to the nozzle (9) from either a container (13) bygravity feed, or by mechanical pumping, or by one of the electrokineticpumping device. The liquid is supplied to the nozzle and the inducedvoltage applied by the electrode (7) before the electric field ismodified to create gaseous ions by the actuation of the flap-valve (2)and/or the capacitor(s) (11). Then, at any time after the spray cloud isdeveloped, the breath-actuated valve and/or the capacitor(s) isactuated, whereupon the droplet trajectories are modified; moving awayfrom their direct flight to the electrode (7), through the requiredangle, say to flow by viscous drag in the air movement caused by normalbreathing. This action is virtually instantaneous due to the extremelylow inertial forces on droplets used for inhalation therapy, which aregenerally less than about 10.0 μm in diameter for drug inhalation.

An alternative method of creating the required induction potential toatomize the liquid and subsequently discharge the droplets beforeimpingement upon the induction electrode is to use an inductionelectrode (14) such as, for example, a ring with two distinctcross-sectional radii of curvature, as shown in FIG. 4. This method maybe used with or without a flap valve (2), or field modifyingcapacitor(s) (11). The larger radius faces toward the nozzle tip, whilstthe smaller radius (say less than about 1.0 mm) faces away from thenozzle (9). It has been found that, by very careful design of the fieldpattern, charged droplets may have sufficient inertial force to passthrough a gap in the electrode (14) without immediate impingement.Although these droplets are then almost immediately forced back toimpinge upon the electrode, they may be prevented from doing so by theneutralizing action of the fast moving gaseous ions. It has been furtherdiscovered that production of gaseous ions by gas breakdown at thesmaller radius of curvature may be delayed by maintaining the fieldstrength at the electrode below the critical value until the chargeddroplets enter the field, whereupon they will increase the fieldstrength to the critical value and immediately trigger the dropletdischarge process.

The critical field strength and shape is a function of: electrodeposition, shape, and voltage; the relative positions and potentials ofthe nozzle and capacitor(s) surfaces and the degree and position ofspace charge potential created by the charged droplets.

It has also been found that the methods of controlled field modification(with time) disclosed herein may be so set as to both discharge and, ifrequired, to recharge the droplets to an optimal value. This could beimportance in, say, ensuring accurate deposition of droplets within ahuman lung, where both the droplet's mass, and its charge havecontrolling influence upon the zones of deposition within the system ofairways through which the droplets pass during inhalation.

A particular example of the device and its operation is shown in FIG. 5:An earthed needle, (15) concentrically located within a non-conductingsleeve (16) allowed liquid to flow (by gravity or other light pressure)to an outlet nozzle (17) where the liquid was exposed to a strongconvergent electric field provided by a high potential supplied to theflat, smooth surface of electrode (18). This resulted in an inducedelectrohydrodynamic (EHD) communition of the liquid emerging fromcapillary nozzle (17).

After the communition was established (and within less than one second)a sharp element (19) of the induction electrode (18) was exposed.

The exposure of (19) above the smooth surface of (18) produced gaseousions of the polarity of the high voltage dc, generator (20). Since theEHD spray cloud was induced from an earthed electrode-nozzle (17), thegaseous ions and the spray droplets have opposing polarities. And as thegaseous ions have much greater mobility in the electric field containingboth droplets and ions, the droplets were bombarded and henceelectrically discharged.

In the experiment described, the distance between tip of nozzle (17) andflat electrode was 30 mm. When the sharp electrode (19) was positionedto discharge the droplets, the distance between tip of nozzle (17) andneedle-tip (19) was 23 mm. The liquid flow-rate was 1.34 μl/sec. Thehigh voltage source was set at a negative potential of 10.7 kilovolts.

The liquid used was 80% ethanol and 20% polyethylene glycol (200),having a viscosity of 2.2 c Poise, a surface tension of 25.0 m N/m, aresistivity of 1.7×10³ ohm.m and a density of 0.86 kg/liter.

The discharging effect was assessed to be essentially 100 per cent.

1. An inhaler for enabling inhaled administration to and via the nasalmucosa, the inhaler comprising a housing having an outlet duct providingan air passageway through which a user can inhale, the housingcontaining: a liquid container having a liquid outlet; and means forapplying a high voltage to cause liquid issuing from the liquid outletto emerge as a jet which breaks up into charged droplets which arecaused, by the act of the user inhaling, to flow towards the outletduct.
 2. An inhaler for enabling inhaled administration to and via thenasal mucosa, the inhaler comprising a housing having an outletproviding an air passageway through which a user can inhale, the housingcontaining: a liquid container having a liquid outlet; and an applicatorof a high voltage to cause liquid issuing from the liquid outlet toemerge as a jet which breaks up into charged droplets which are caused,by the act of the user inhaling, to flow towards the outlet duct.
 3. Aninhaler for enabling inhaled administration, the inhaler comprising ahousing having an outlet duct defining a passageway through which aircan be drawn by inhalation on the part of a user, the housingcontaining: a capillary nozzle; a container for containing a quantity ofliquid to be supplied to the capillary nozzle; and a voltage producerfor producing a voltage in the liquid prior to issue from the containervia the capillary nozzle to expose the liquid to an electric field tocause comminution of the liquid emerging from the capillary nozzle toproduce a spray of electrically charged droplets, where, when a userinhales via the outlet duct, electrically charged droplets are suppliedvia the outlet duct for deposition in the user's airways.
 4. An inhalerfor enabling inhaled administration of a medicament to and via the nasalmucosa, the inhaler having a housing having an outlet duct defining apassageway through which air can be drawn by inhalation by a user, thehousing containing: a liquid container containing a quantity of liquidand having an outlet; and a voltage applier for applying a voltage tothe liquid before it emerges from the outlet to subject the liquid to anelectric field to cause comminution of liquid emerging from the outletto produce a spray of electrically charged droplets, wherein, when auser inhales via the outlet duct, electrically charged droplets aresupplied via the outlet duct and into the user's airways.
 5. An inhalerfor enabling inhaled administration of a medicament to and via the lowerrespiratory tract, the inhaler having a housing having an outlet ductdefining a passageway through which air can be drawn by inhalation by auser, the housing containing: a liquid container containing a quantityof liquid and having an outlet; and a voltage applier for applying avoltage to the liquid before it emerges from the outlet to subject theliquid to an electric field to cause comminution of liquid emerging fromthe outlet to produce a spray of electrically charged droplets, wherein,when a user inhales via the outlet duct, electrically charged dropletsare supplied via the outlet duct and into the user's airways.
 6. Aninhaler for enabling inhaled administration to and via the nasal mucosa,the inhaler comprising a housing having an outlet duct providing an airpassageway through which a user can inhale, the housing containing: aliquid supplied for containing a quantity of liquid, the liquid supplierhaving a non-conductive sleeve with an outlet and also having a needlelocated within the sleeve; and an electric field generator forgenerating an electric field at the sleeve outlet to cause liquidissuing from the sleeve outlet to emerge as a jet which breaks up intocharged droplets for supply, in response to the user inhaling, to andvia the nasal mucosa, the electric field generator including a voltageapplier for applying a voltage to the liquid prior to issue from theoutlet.
 7. An inhaler for enabling inhaled administration to and via thenasal mucosa, the inhaler comprising a housing having an outlet ductproviding an air passageway through which a user can inhale, the housingcontaining: a liquid supplier for containing a quantity of liquid, theliquid supplier having an outlet; and an induction charged adapted toinduce a voltage at the liquid supplier outlet to cause liquid issuingfrom the outlet to emerge as a jet which breaks up into charged dropletsfor supply to a zone of deposition within the user's airways when air isdrawn through the passageway by inhalation by the user.
 8. An inhalerfor enabling inhaled administration to and via the nasal mucosa, theinhaler comprising a housing having an outlet duct providing an airpassageway through which a user can inhale, the housing containing: aliquid supplier for containing a quantity of liquid, the liquid supplierhaving an outlet; and a syringe pump for causing liquid to be pumped tothe liquid supplier outlet; and a voltage applier for applying a voltageto the liquid prior to issue from the liquid supplier outlet so as tosubject the liquid to an electric field to cause comminution of liquidemerging from the outlet to produce a spray of electrically chargeddroplets to be supplied to a zone of deposition within the user'sairways when air is drawn through the passageway by inhalation by theuser.